PROCESS AND DEVICE FOR OIL STABILITY MEASUREMENT

Abstract: The invention concerns a method and a device for determination of the stability or storability of oil. In the method the stability of oil is determined by measuring the intensity of light scattering from the oil surface, when an asphaltene-flocculating liquid is added to the oil sample for determining the stability of the oil. In an advantageous embodiment of the method the intensity of scattered light is directed onto the surface of the oil sample by using a suitable prism. The invention allows implementation of a fully automatically operating analyzer for determining the stability of oil. Using the invention a closed measuring system is brought about that solves the explosion protection problem which is important in oil refining.

Description: Process and device for oil stability measurement The invention concerns a method and a device for determination of the stability or storability of oil. Oil refining gives rise to dark heavy high-boiling oil fractions and their mixtures, of which bitumen and heavy fuel oil are made, among other things. The use and storability of these oil raffinates are impaired by the poor solubility or precipitation of asphaltenes in the oil. The precipitation ability of asphaltenes determines the stability or storability of the oil, and this depends both on the oil production process used and on the raw materials. In particular, the heat-cracking unit which is used today affects the precipitation ability of asphaltenes. Hereby the oil refining process should be controlled so that the heavy fuel oil obtained as the basic product of the unit will be stable. The stability of oil has traditionally been determined from samples taken from the oil, i.a. by so-called flocculation methods (for example, the Shell method; Flocculation ratio of bitumen and fuel oil). These methods are based on paper chromatography and on visual perceptions in this connection. Getting a result takes from 1/2 to 6 hours when using this method. Automatic on-line analyzers have been developed which are based, for example, on an observation of the oil product's asphaltene content either in connection with the production process or on a measurement of laboratory samples. In an automatic on-line analyzer of this type a computer-controlled process analyzer automatically takes a sample from the desired product flow at determined intervals and puts out a parameter indicating the stability to the process control room at determined intervals of time, for example, 10 minutes. However, in these methods it has been a problem that the measurement results are too varied or the measurement methods have been too slow for adjusting the process. Another problem with the known methods is that the measuring cell used for measuring has been open. As measurements can not be done in a closed measuring system, handling of the sample has been cumbersome and protection against explosion, which is very important in oil refining, has been problematic. The invention aims at bringing about an improvement in the known methods of determining the stability or storability of oil. A more closely specified aim of the invention is to bring about a method of determining the stability of oil directly from the oil surface, so that the obtained measurement result can be used in controlling the oil quality or in controlling the production. It is an objective of the invention to bring about a method allowing a fully automatically operating analyzer for determining the stability of oil. Another objective of the invention is to bring about a closed measurement system. In a closed measurement system separate sample handling is avoided and the problem of protection against explosions, which is very important in oil refining, has been solved. The above-mentioned objectives are achieved through a new method and device, which are characterized by the features presented in the independent patent claims. The invention is based on the surprising finding that the stability of oils can be determined promptly and reliably by measuring the intensity of light scattering from the oil surface. It was also found surprisingly that by designing the analyzer's measuring cell for oil stability measurement so that measuring takes place through a prism, the drawbacks of methods representing the state of the art could be avoided. Several advantages are obtained by using a prism in a measuring device in accordance with the invention. Using the prism it is possible to direct the light ray arriving in the studied oil sample directly to the desired point without any harmful reflections. Likewise, the desired part of the light leaving the oil sample can be directed to an indicator. When a prism is used there is no open oil sample surface in the measuring device, so the measuring device can be entirely closed. When using the method according to the invention for measuring the stability of heavy oil fractions derived from petroleum or the stability of their mixtures, a diluent such as, for example, toluene, xylene or some other diluent may be added to the oil and at the same time or afterwards asphaltene-flocculating hydrocarbon is added to the oil, such as pentane, hexane, heptane, octane or some other, until the intensity of the scattering light ray increases sharply, thus indicating the flocculation point of the asphaltene. The stability of the oil being measured can be calculated with one or several determinations and expressed with a figure indicating the stability, for example, as xylene equivalents. The method now developed makes possible an optical determination of the stability of oil from the oil surface. The result can be used for controlling the oil production or for quality monitoring. An analyzer functioning with the method according to the invention can be fully automated even for sampling and result computing, which allows the important use of a quality magnitude in the automatic follow-up of the oil production and in the process control. The invention is explained in greater detail by referring to the principal solution of the method according to the invention, which is shown in the figure in the enclosed drawing, but to which the invention is not intended to be limited. Figure 1. Measurement of oil stability based on light scattering. Figure 2. Measurement of oil stability based on light scattering and using a prism. Figure 3. Measurement of oil stability based on light reflection and using a prism. Figure 1 shows a measurement of the stability of oil based on light scattering. Reference number 10 in the figure indicates the measuring device in general. The measuring device 10 comprises a light source 11, a sample vessel 12, in indicator 14 and equipment 15 for feeding a diluent or flocculating additive. A light ray 16 is direceted at any angle from light source 11 onto the surface of oil 13 in sample vessel 12, whereby a part of the arriving light ray 16 is reflected as a light ray 17 reflected from the oil surface and a part is scattered as a light ray 18 scattered from the oil surface and from the particles it contains, which latter light ray is detected by indicator 14 at any angle. When measuring the stability of oil a flocculating additive is supplied into sample vessel 12 from feeding equipment 15. The monochromatic light ray 16 and the normal 19 to the surface of oil sample 13 form an angle a of any value. The light ray 18 scattered from the oil surface and the normal 19 to the surface of oil sample 13 form an angle a of any value. When measuring device 10 according to Figure 1 is used for measuring the stability of heavy oil fractions derived from petroleum or the stability of their mixtures, a diluent, such as toluene, xylene or some other similar diluent is preferably though not necessarily added to the oil in sample vessel 12. Then asphaltene-flocculating hydrocarbon, for example, pentane, heptane, octane or some similar is supplied from feeding equipment 15 and measures by balance 20 into sample vessel 12, until the intensity of the scattered light 18 rises sharply, thus indicating the flocculation point of the asphaltene. The stability is calculated with the aid of one or several determinations and it is expressed, for example, as xylene equivalents, known previously as a measure of stability. When the method in accordance with the invention is used for measuring contents of substances insoluble in heavy oil fractions derived from petroleum or in their mixtures, the arriving light ray 16 is directed onto the oil product surface and onto the oil layer under the surface, whereby the intensity of light 18 scattered from the oil product surface and from inside the oil product will indicate the content of particles in the oil. Figure 2 shows a measurement of the stability of oil based on light scattering and using a prism. The measuring device comprises a light source 21, a sample chamber 22, an" indicator 24 and feeding channels 25 for supplying oil and a diluent or a flocculating additive. The light ray 26 arriving from light source 21 hits the prism 23, thus being directed from its surface onto the interface of the prism and the sample to be examined, from which interface part of the light is scattered as a reflected light ray 27 to indicator 24. As in the device shown in Figure 1, the measuring device is also associated with a piece of equipment, wherein a diluent or a flocculating additive is added to the oil to be examined. This mixture is supplied through feeding channel 25 into the sample chamber and further to leave the measuring device by way of exhaust channel 28. Figure 3 shows a measurement of the stability of oil based on light reflection and using a prism. The measuring device comprises a light source 31, a sample chamber 32, a prism 33, an indicator 34, feeding channels 35 and exhaust channels 36 for feeding oil and a diluent or a flocculating additive. Light ray 36 arriving from light source 31 hits prism 33, passing from its surface onto the interface of the prism and the sample to be examined, from which interface part of the light is reflected as a light ray 37 to the indicator 34. This measuring device, too, like the device in accordance with Figures 1 and 2, may be associated with a piece of equipment wherein a diluent or a flocculating additive is added to the oil being examined. This mixture is fed through feeding channel 35 into the sample chamber and further to leave the measuring device by way of exhaust channel 38.

Claims: Claims 1. Method of determining the stability of oil, characterized in that a light ray (16, 26, 36) is directed from a light source (11, 21, 33) onto the surface of the oil sample being examined and in that the intensity of a light ray (18, 27, 37) scattered or reflected from an oil sample in a sample vessel (12, 22, 32) indicates the stability of the oil. 2. Method as defined in claim 1, characterized in that the light ray (16) is directed onto the surface of the oil sample by using a suitable prism. 3. Method as defined in claim 2, characterized in that the point angle of the prism is 90". 4. Method in accordance with any claim 1 - 2, characterized in that when determining the stability of oil, especially of heavy oil fractions derived from petroleum or of their mixtures, an asphaltene-flocculating liquid is added to the oil sample (13). 5. Method as defined in claim 4, characterized in that pentane, hexane, heptane, octane or any liquid having similar properties is used as the liquid for flocculating asphaltenes. 6. Method as defined in claim 4 or 5, characterized in that asphaltene-flocculating liquid is added until the intensity of the scattered or reflected light (18, 27, 37) rises sharply thus indicating the flocculation point of the asphaltene. 7. Method as defined in claims 1 - 6, characterized in that when determining the stability parameter or xylene equivalent of oil, especially of heavy oil fractions derived from petroleum or of their mixtures, toluene, xylene or some similar diluent is used and it is added before or simultaneously with the focculating liquid. 8. Method as defined in claims 1 - 7, characterized in that the oil sample is agitated during the determination. 9. A device for determining the stability of oil, characterized in that the device has a light source (11, 21, 31) for directing a light ray (16, 26, 36) onto the surface of the oil sample being examined, a sample vessel (12) containing an oil sample from which a light ray (18, 27, 37) is scattered or reflected, and an indicator (14, 24, 34) for measuring the light intensity. 10. Device as defined in claim 9, characterized in that it has a prism (23) for directing a light ray (26) onto the surface of the oil sample and further to an indicator (24).

Inventors: PILVIOE OLLI, TOLVANEN ILKKA, WALDVOGEL JUERG, PILVIOE, OLLI, TOLVANEN, ILKKA, WALDVOGEL, JUERG
Applicants: NESTE OY, PILVIOE OLLI, TOLVANEN ILKKA, WALDVOGEL JUERG, PILVIOE, OLLI, TOLVANEN, ILKKA, WALDVOGEL, JUERG
Application year: 1994
Main classification: G01N21
IPC codes: G01N21, G01N33